The present invention relates to an ITO (compound oxide having indium and tin as primary components: In2O3—SnO2) sputtering target to be used in forming an ITO film.
An ITO film is widely used as a transparent electrode (film) of a display device; mainly a liquid crystal display.
As a method of forming this ITO film, ordinarily employed is a method generally referred to as a physical vapor deposition method such as the vacuum deposition method or sputtering method. Particularly, the magnetron sputtering method is often employed for forming such ITO film from the perspective of operability and stability of the film.
The formation of film with the sputtering method is performed by physically colliding a positive ion such as Ar ion to a target established in the negative electrode, discharging materials composing the target with such collision energy, and laminating films of approximately the same composition as the target material on the substrate on the opposing positive electrode side.
The coating method employing the sputtering method is characterized in that it is capable of forming from a thin film of angstrom units to a thick film of several ten μm at a stable deposition speed by adjusting the processing time, power supply, and so on.
A particular problem in forming an ITO film is the generation of minute protrusions referred to as nodules on the target surface during the sputtering operation, which increases pursuant to the increase in sputtering time.
Nodules generate arcing during sputtering, and fragments of nodules or reducing substances of ITO become particles and are dispersed. When such dispersions adhere to the ITO film, that portion will become defective, and cause the productivity to deteriorate.
Due to the foregoing reasons, upon the actual manufacture, it is necessary to periodically remove the nodules generated on the target surface. This, however, causes problems in the considerable deterioration of productivity, and a target generating few nodules is being demanded.
Conventionally, in order to reduce nodules, the target surface was purified or smoothed, or the high densification of the target was sought. The most effective method was to uniformly disperse tin oxide in the raw material powder (e.g., refer to Patent Document 1).
As a result of this method, it is possible to reduce as much as possible the segregation in the tin oxide target having low conductivity and low sputter etching speed, and thereby reduce defects in the ITO film caused by arcing resulting from the generation of nodules.
Nevertheless, in recent years, for the advancement of high resolution of flat panel displays and improvement in the production yield of ITO films, even small defects can no longer be ignored, and demands for further reducing the arcing are increasing.
[Patent Document 1] International Publication No. WO2002072912